Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing a first image in a sequence according to the claimed design;

FIG. 2 is a front view showing a second image in the sequence according to the claimed design; and,

FIG. 3 is a front view showing a third image in the sequence according to the claimed design.

The appearance of the image transitions sequentially between the images shown in FIGS. 1-3. The process or period in which one image transitions to another image forms no part of the claimed design. The shading depicts a contrast in appearance. The outermost broken lines illustrate an electronic device, which is the environment of the design, and form no part of the claim. The dot-dot-dash broken lines represent a symbolic break in vertical dimension. The appearance of any portion of the graphical user interface between the break lines forms no part of the claimed design. The remaining broken lines illustrate portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 